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United States Patent |
6,259,708
|
Cheng
,   et al.
|
July 10, 2001
|
System and method of transmitting voice over digital subscriber line
Abstract
A system for digitizing voiceband signals at the remote terminal (20) of a
Digital Subscriber Line (DSL) connection and embedding the digitized
voiceband component into an active DSL data stream using a DSL modem (24).
Voiceband transmissions between the remote terminal (20) and the central
office call switching equipment (1) occur in the analog domain when the
DSL modem (28) is OFF and in the digital domain when the DSL modem (28) is
ON with the digital voiceband signals transmitted over a DSL link.
Preferably, the remote terminal (20) can drive a real analog telephone
(30) by providing battery feed, ring-trip detection, off-hook detection
and ringing generation (60) In-house 4-wire lines pairs (21, 23) are
configured between the modem, telephones and computer or home network to
permit all digital transmission from the subscriber to the central office.
Inventors:
|
Cheng; Yaqi (Las Vegas, NV);
Franz; Warren L. (Dallas, TX);
Chen; Walter Y. (Franklin, MA);
Polley; Michael O. (Richardson, TX)
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Assignee:
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Texas Instruments Incorporated (Dallas, TX)
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Appl. No.:
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244606 |
Filed:
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February 4, 1999 |
Current U.S. Class: |
370/493; 370/201; 370/271; 370/521; 370/524; 375/295; 375/377 |
Intern'l Class: |
H04J 015/00; H04J 003/00; H04L 012/16; H04L 027/04; H04L 023/00 |
Field of Search: |
370/493,535,524,360,468,110,112,118
375/211,295,260,222,377
|
References Cited
U.S. Patent Documents
5410343 | Apr., 1995 | Coddington et al. | 348/7.
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5479447 | Dec., 1995 | Chow et al. | 375/260.
|
5764628 | Jun., 1998 | Davis et al. | 370/271.
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5787088 | Jul., 1998 | Dagdeviren et al. | 370/493.
|
5883941 | Mar., 1999 | Akers | 379/93.
|
5910970 | Jun., 1999 | Lu | 375/377.
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5991311 | Nov., 1999 | Long et al. | 370/524.
|
6002722 | Dec., 1999 | Wu | 375/295.
|
Other References
Reeve, Subscriber Loop Signaling and Transmission Handbook: Digital (IEEE,
1995), pp. 60-63.
Reeve, Subscriber Loop Signaling and Transmission Handbook: Analog (IEEE,
1992), pp. 197-211.
|
Primary Examiner: Vu; Huy D.
Assistant Examiner: Phan; M.
Attorney, Agent or Firm: Moore; J. Dennis, Brady, III; W. James, Telecky, Jr.; Frederick J.
Parent Case Text
This application claims priority under 35 USC .sctn. 119(e)(1) of
provisional application number 60/073,666, filed Feb. 4, 1998.
Claims
What is claimed is:
1. In a communications system, a remote terminal for communicating
voiceband signals over a digital subscriber line (DSL), the DSL coupled to
a wire line pair connection providing a communications link from at least
one voiceband device and one digital data device to a central office
facility, the remote terminal comprising:
a voice frequency interface with first and second terminals, said first
terminal coupled to said voiceband device;
a digital data interface with first and second terminals, said first
terminal coupled to said digital data device;
a means of digitizing voiceband signals having an input terminal coupled to
said second terminal of said voice frequency interface and an output
terminal; and
a DSL compliant device with first, second and third terminals, said first
terminal coupled to said digital data interface for communicating with
said digital data device, said second terminal coupled to said output
terminal of said means of digitizing voiceband signals and said third
terminal coupled to said wire line pair connection;
wherein said DSL compliant device is configured to accept as input the
digitized voiceband signal components from said means of digitizing
voiceband signals and intersperse them into a DSL signal stream
transmitted to the central office facility.
2. The remote terminal according to claim 1 further comprising a high
frequency interface interspersed between said third terminal of said DSL
compliant device and said wire line pair connection.
3. The remote terminal according to claim 2 wherein said high frequency
interface comprises a high pass filter tuned to pass DSL signal
components.
4. The remote terminal according to claim 1 further comprising a first
switching mechanism interspersed between said DSL compliant device and
said wire line pair connection.
5. The remote terminal according to claim 4 wherein said switch mechanism
includes first, second and third terminals, said first terminal coupled to
said second terminal of said voice frequency interface, said second
terminal coupled to said third terminal of said DSL compliant device and
said third terminal coupled to said wire line pair connection.
6. The remote terminal according to claim 5 wherein said switch mechanism
allows said voice band device to operate in a life line state by making
establishing a connection between said first and third contacts of said
switch mechanism.
7. The remote terminal according to claim 5 wherein said switch mechanism
causes a connection to exist between said second and third contacts of
said switch mechanism.
8. The remote terminal according to claim 1 wherein said means of
digitizing voiceband signals includes an analog to digital converter
capable of producing a 64 kbps digitized voiceband data stream.
9. The remote terminal according to claim 1 wherein said means of
digitizing voice band signals is configured to present the typical line
characteristics found over a twisted pair connection of the PSTN.
10. The remote terminal according to claim 7 wherein said voice frequency
interface presents a 48 volt line voltage to said voiceband device when a
connection exists between said second and third contacts of said switch
mechanism.
11. The remote terminal according to claim 1 further comprising a wire
concentrator interspersed between said voice frequency interface adjacent
said digital data interface and said voiceband and digital data devices.
12. The remote terminal according to claim 11 wherein said wire
concentrator is configured to switch signals away from said voiceband
device to said digital data interface.
13. A central office call switching device comprising:
a line interface;
a voice frequency interface for communicating analog signals to and from an
analog switching system;
a signal converter with analog and digital terminals, said analog terminal
coupled to the voice frequency interface, the signal converter for
converting analog signals received from the voice frequency interface into
digital data for presentation at its digital terminal, and for converting
digital signals received at its digital terminal into analog signals for
forwarding to the voice frequency interface;
a digital subscriber line (DSL) compliant device with first, second and
third terminals, said first terminal coupled to said digital terminal of
said signal converter;
a digital interface with first and second terminals, said first terminal
coupled to said third terminal of said DSL compliant device, said second
terminal providing a signal pathway to at least one digital backplane; and
a switching mechanism for coupling the line interface to the second
terminal of the DSL compliant device in a DSL operating state, and for
coupling the line interface to the voice frequency interface in a
voiceband operating state.
14. The central office switching device according to claim 13 further
comprising an analog switching system coupled to the voice frequency
interface.
15. The central office switching device according to claim 13 further
comprising a high frequency interface coupled between said DSL compliant
device and said switching mechanism.
16. The central office call switching device according to claim 15 wherein
said high frequency interface includes a DSL band pass filter.
17. A communications network for communicating voiceband signals over a
Digital Subscriber Line (DSL) transmission link comprising:
a remote terminal configured to receive analog voiceband signals from at
least one voiceband device, convert them into corresponding digital
signals and embed them into the DSL data stream transmitted over said
transmission link, comprising:
a voice frequency interface with first and second terminals, said first
terminal coupled to the voiceband device;
a digital data interface with first and second terminals, said first
terminal coupled to a digital data device;
means for digitizing voiceband signals, having an input terminal coupled to
said second terminal of said voice frequency interface and an output
terminal; and
a DSL compliant device, having a first terminal coupled to said digital
data interface for communicating with said digital data device, a second
terminal coupled to said output terminal of said means of digitizing
voiceband signals, and a third terminal coupled to said wire line pair
connection, for interspersing the digitized voiceband signal components
from said means of digitizing voiceband signals into a DSL signal stream
to be transmitted over the DSL transmission link; and
a central office containing call switching equipment configured to
communicate with said remote terminal over said DSL transmission link,
said call switching equipment comprising:
a voice frequency interface for communicating analog signals to and from an
analog switching system;
a signal converter having an analog terminal coupled to the voice frequency
interface, the signal converter for converting analog signals received
from the voice frequency interface into digital data for presentation at a
digital terminal, and for converting digitized voice band signals
contained in said DSL data stream and received at its digital terminal to
corresponding analog voice band signals for forwarding to the voice
frequency interface;
a digital subscriber line (DSL) compliant device having a first terminal
coupled to said digital terminal of said signal converter;
a digital interface having a first terminal coupled to a second terminal of
said DSL compliant device, and having a second terminal providing a signal
pathway to at least one digital backplane; and
a switching mechanism for coupling the line interface to a third terminal
of the DSL compliant device in a DSL operating state, and for coupling the
line interface to the voice frequency interface in a voiceband operating
state.
18. The communications network according to claim 17 wherein said remote
terminal is able to present the transmission line characteristics of
twisted pair lines in a typical Public Switched Telephone Network (PSTN)
installation.
19. The communications network according to claim 17 wherein said remote
terminal is capable of switching between an all DSL operating state and a
voiceband operating state.
20. The communications network according to claim 17 wherein call switching
equipment contains a first interface to a digital backplane network and a
second interface to a switched analog network.
Description
TECHNICAL FIELD
The present invention relates in general to communications using existing
telephone wire and more particularly to a system that digitizes voiceband
signals and transmits them over a digital subscriber line (DSL) using a
DSL modem or other similar DSL device.
BACKGROUND OF THE INVENTION
The increased use of telephone twisted pair wiring for data communications
has resulted in a push for faster modems and improved signaling protocols
compatible with the public switch telephone network (PSTN). An example
includes the emerging variety of the DSL communications protocols
including asymmetric digital subscriber line (ADSL), symmetric digital
subscriber line (SDSL), high bit rate digital subscriber line (HDSL), and
very high rate digital subscriber line (VDSL). Each DSL variant represents
a different transmission speed over possibly different distances of copper
pair wiring usually for different applications.
In principle, a DSL modem and a plain old telephone system (POTS) or other
voiceband device can operate simultaneously over the same twisted pair
connection since they use different frequency bands. The connection,
however, of a POTS to the same wire line pair as a DSL modem can suffer
from several problems that result from the change in input impedance of
the POTS equipment as it is added to the line. In essence, most POTS
equipment is not designed to handle frequencies outside the voiceband of
300-3.4 kHz. In addition, POTS equipment often contains nonlinear
components that may create intermodulation and harmonic interferences.
Examples of such nonlinear components include Zener diodes, transistors,
varistors, triacs, and other devices used for overvoltage protection,
sidetone generation and overvolume protection.
As the shift to all digital communications continues, the POTS, due to its
large installed base and widespread application may represent the final
analog domain of telephony. Eventually, the industry may adopt a network
that is entirely digital and DSL will eventually be the standard of
choice. However, with the rapid growth of the Internet, high speed DSL
modems might first dominate the telephone wires. One of promised DSL
techniques is Asymmetrical Digital Subscriber Lines (ADSL). ADSL is an
ANSI standard (T1E1.4-T1.413) issued in 1995 which presents the electrical
characteristics of the Asymmetric Digital Subscriber Line signal appearing
at the network interface.
While a known prior art technology, called Digital Pair Gain Device, can
utilize one wire line pair to carry multiple voice channels, it requires
that the connection be routed through an Integrated Service Digital
Network (ISDN). The central office terminal emulates a telephone set for
ring detection and hold purposes. On the other hand, the remote terminal
at home drives a real analog phone by providing battery feed, off-hook
detect, ring-trip detect, and ringing generation. The system requires a
high frequency modem solely for its voice channels.
While ISDN is another typical DSL application, its limited data rate is not
good for future Internet access. A fully digital telephony solution based
on DSL, however, would be more advantageous. The integration of high speed
modems and digital voice is important in today's consumer market and for
applications such as 6-Mbps ADSL and voice over IP.
SUMMARY OF THE INVENTION
The invention provides a system for digitizing voiceband signals at the
remote end of a Digital Subscriber Line (DSL) connection and embedding the
digitized voice component into an active DSL data stream using a DSL
modem. Voiceband transmissions between the remote terminal and the central
office occur in the analog domain when the DSL modem is OFF and in the
digital domain when the DSL modem is ON with the digital voiceband signals
transmitted over a DSL link. With the DSL link active, the remote terminal
communicates directly with the analog telephone equipment connected to the
in-house 4-wire lines by providing battery feed, ring-trip detection,
off-hook detection and ringing generation. In-house 4-wire lines provide
connections between the DSL modem, telephones and computer or home
networking equipment. A switching scheme enables a powered up DSL modem to
control the analog equipment.
According to one embodiment, disclosed is a remote terminal for
transmitting voiceband signals over a digital subscriber line (DSL) with
the DSL coupled to a wire line pair connection providing a communications
link from at least one voiceband device (such as a standard subscriber
side telephone) and one digital data device (such as a desktop computer)
to a central office facility. The remote terminal comprises a voice
frequency interface with first and second terminals, the first terminal
coupled to the voiceband device. A digital data interface with first and
second terminals is also provided, the first terminal coupled to the
digital data device. The device also includes a means of digitizing
voiceband signals, such as an analog-to-digital signal converter, with an
input terminal coupled to the second terminal of the voice frequency
interface and an output terminal.
The device further includes a DSL compliant device, such as a DSL modem,
with first, second and third terminals, the first terminal being coupled
to the digital data interface for communicating with a digital data device
such as a computer, the second terminal coupled to the output terminal of
the means of digitizing voiceband signals and the third terminal coupled
to the wire line pair connecting the customer premise to the central
office. Essentially, the DSL compliant device is configured to receive
digitize voiceband signals and intersperse them into the upstream DSL
signal stream to the central office facility. The means for digitizing
voice band signals is configured to present the same line conditions to
the voice band component as it expects to see when the DSL compliant
device is turned OFF.
According to another embodiment, disclosed is a central office call
switching device comprising a line interface and a signal converter with
analog and digital terminals, the analog terminal coupled to the line
interface in a first operating state of the device. A digital subscriber
line (DSL) compliant device with first, second and third terminals is also
provided, the first terminal coupled to the digital terminal of the signal
converter, the second terminal coupled to the line interface in a second
operating state.
The central office call switching device also includes a digital interface
with first and second terminals, the first terminal coupled to the third
terminal of the DSL compliant device, the second terminal providing a
signal pathway to at least one digital backplane, such as an Internet
Protocol (IP) network. A voice frequency interface with first and second
terminals is further provided, the first terminal coupled to the analog
terminal of the signal converter.
Further disclosed are wiring configurations for coupling a remote terminal
capable of digitizing voiceband signals and transmitting them in a DSL
data stream utilizing the wire line pairs existing on the subscriber side
of the network. According to one configuration, a voice frequency
interface has a first terminal coupled to the subscriber POTS and a second
terminal to a digitizing voiceband function through an existing, often
unused, wire line pair. The switching mechanism, depending on the state of
the remote terminal, can create a signal path from the POTS through a DSL
compliant device in the remote terminal. If the remote terminal DSL
complaint device is powered down, the switching mechanism will bypass the
remote terminal entirely for normal voiceband operation.
According to another configuration, the voice frequency interface is split
into two interfaces with the POTS coupled to one of the interfaces and a
digital processing system to the second interface. Instead of coupling the
processing system to the DSL device, the switching mechanism operates the
transitions between the all-DSL state and the normal POTS voiceband
operation.
According to another embodiment, the POTS is permanently coupled to the DSL
device in the remote terminal and the DSL compliant device (DSL modem) at
the subscriber side is always turned ON with the second wire line pair
never used.
BRIEF DESCRIPTION OF THE DRAWINGS
Other aspects of the invention including specific embodiments are
understood by reference to the following detailed description taken in
conjunction with the appended drawings in which:
FIG. 1 is a block diagram of the central office and remote terminal
equipment according to the invention;
FIG. 2 illustrates the general overview of the voiceband line card for the
central office;
FIG. 3 illustrates the digital voiceband portion of the remote terminal;
FIG. 4 illustrates the wiring scheme of an in-house four wire phone line
for the remote terminal configuration;
FIG. 5 illustrates the wiring scheme of the in-house four wire phone line
for the RT configuration when the network interface is connected to the
same wire line pair;
FIG. 6 illustrates the wiring scheme of the in-house four wire phone line
for the remote terminal configuration where the subscriber line is
connected to a second wire line pair; and
FIG. 7 illustrates the wiring scheme for the remote terminal where the DSL
compliant device and voiceband device use the same wire line pair but the
voice frequency interface behaves as a low pass filter.
References in the detailed description correspond to like references in the
figures unless otherwise indicated.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention provides a general architecture and system for
transmitting voiceband signals within a digital subscriber line (DSL) data
stream. The architecture may be adopted and utilized within an ADSL
transmission unit (ATU), either central or remote, to provide end-to-end
communications between a subscriber and a central office facility over a
wire line pair. The switching mechanism provides the means by which a DSL
modem can disconnect the local telephone equipment from the incoming
telephone line and provide power and other typical line conditions to the
telephone equipment.
With reference to FIG. 1, therein are shown block diagrams of both the
central office (CO)1 and remote terminal (RT) 20 according to the
invention. A two wire outside wire pair 6 provides the physical connection
to the customer premise equipment on the subscriber side of the network.
The wire line pair 6 is coupled to the CO call switching equipment within
the CO 1. A high frequency interface 11 is coupled to the wire line pair 6
through a switching mechanism 5.
In essence, the switching mechanism 5 provides a means of altering the
signal path of signals flowing through the wire line pair 6, either to the
DSL compliant device 10 (which is probably a DSL modem or linecard)
through the high frequency interface 11, or to both the voice frequency
interface 4 and the DSL compliant device 10. Typically, communications
between the CO 1 and the remote terminal 20 are bidirectional, i.e., both
in the upstream and downstream directions. For the purpose of this
description, the terms CO and CO call switching equipment will be used
interchangeably and associated to reference numeral 1 of FIG. 1.
Typically, the wire line pair 6 comprises a single twisted copper wire line
pair of the type found in many Public Switched Telephone Networks (PSTN).
The wire line pair 6 can be switchingly engaged to the analog terminal 3
of the digital voiceband unit (DVB) 7 through the switching mechanism 5.
In this configuration, the switching mechanism 5 places the central office
switching equipment 1 in a normal Voiceband (VB) operating state. In the
VB state, analog signals within the voiceband (approximately 0-3.4 kHz)
are switched from one voiceband device, such as a POTS 30, to a second
voiceband device (not shown) through the CO 1 using switching system 2.
The operation of the switching system 2 within the CO 1 is well known to
those familiar with the facilities of the PSTN.
In the second operating state of the call switching equipment 1, the remote
terminal 20 is transmitting voiceband signals embedded in a DSL data
stream. Thus, the wire line pair 6 is coupled to terminal 12 of the high
frequency interface 11 establishing an all DSL operating state within the
CO call switching equipment 1. In the all DSL operating state, all signals
over the wire line pair 6 enter the high frequency interface 11 (including
digitized voiceband signals embedded in the DSL signal stream) and are
received by the DSL compliant device 10. The DSL compliant device 10 can
be a DSL modem, linecard, rack or other similar communications device
within the CO 1.
In a normal operating state, or voiceband (VB) operating state, the
switching mechanism 5 creates a signal path between the wire line pair 6
and the analog terminal 3 of the DVB 7. The VB operating state is the
default condition of the network when the DSL compliant device 28 of the
remote terminal 20 is turned OFF. Thus, the switching mechanism 5 connects
the signals of the wire line 6 either to the DSL compliant device 10 or
the voice frequency interface 4 through analog terminal 3.
The main function of the DVB 7 is to create a digital data representation
of analog signals which arrive over the analog terminal 3 from the
switching system 2 as well as to convert digitized voiceband signals
transmitted over the DSL link to their corresponding analog counterpart
that can be sent to the voice frequency interface through terminal 41.
This permits connection of the analog side of the switching system 2 with
the all digital side from the CO 1 which extends to the subscriber when
the DSL device 28 in the remote terminal 20 is turned ON.
The signal path 13 couples the digital terminal of the DVB 7 to a DSL
compliant device 10 within the CO switching equipment 1. In the all DSL
operating state, the DVB 7 and DSL compliant device 10 provide a way of
digitizing the analog signals arriving from the switching system 2 and
then embedding and transmitting the digitized voiceband in a DSL data
stream transmitted over the wire line pair 6 leading to the remote
terminal 20.
DVB 7 and the DSL compliant device 10 also provide a similar
digital-to-analog function in the upstream direction as digitized
voiceband signals received from the remote terminal 20 over the DSL link
are converted to corresponding voiceband signals which are directed to the
analog voice frequency interface 4. The digital interface 9 provides the
connection mechanism to the digital back plane 8 which can lead, for
example, to an Internet service provider or other digital protocol
network. Likewise, in the upstream direction, VB signals on the analog
terminal 3 are directed to the voice frequency interface 4 which provides
the routing mechanism to the switching system 2 leading to a PSTN (not
shown). The switching system 2 represents the typical switching facilities
of the PSTN that permits switched connections to be established among
users of the traditional Plain Old Telephone System (POTS) 30.
The remote terminal 20 is shown in the bottom half of FIG. 1 as having a
similar configuration to the central office switching equipment 1. In
particular, the other end of the wire line pair 21 enters the remote
terminal 20 through the switching mechanism 22 that creates the
appropriate signal path depending on the operating state of the remote
terminal 20. Where the remote terminal 20 operates in the all DSL
operating state, the switching mechanism 22 creates a signal path through
the high frequency interface 27 leading to the DSL compliant device 28
within the remote terminal 20. As before, the DSL compliant device 28 can
be any one of various DSL devices including DSL modems, transceivers and
other similar equipment.
The high frequency interface 27 provides a DSL pass band function centered
about those frequencies within the DSL spectrum. The frequencies in the
high frequency interface can be fixed or can be adaptively selected. Next,
digital signals from the wire line pair 21 reaching the high frequency
interface 27 are received by the DSL compliant device 28 where they are
converted and relayed to either the digital voiceband unit (DVB) 24 or the
digital interface 29 depending on the signal content of the incoming
signal stream.
In this way, digitized voiceband signals can be embedded within a DSL data
stream and transmitted using the DVB 24 over signal path 32. The DVB 24
receives digital representations of voiceband signals and converts them
into analog equivalent signals which are output on the analog terminal 23
via signal path 62 and received by the voice frequency interface 25
leading to the wire concentrator 26 within the subscriber premises.
The remote terminal 20 includes a voice frequency interface 25 and a
digital interface 29 to the wire concentrator 26. In one embodiment, the
wire concentrator 26 comprises the already existing telephone wiring which
permits the remote terminal 20 to utilize the existing installation at a
customers home or business. In another embodiment, the wire concentrator
26 is specifically designed (see FIGS. 4 through 7) and configured to
isolate the voiceband device 30 from the digital data device 31.
The subscriber POTS equipment 30 in the customer premises is coupled to the
wire concentrator 26 in either operating state of remote terminal 20. The
POTS equipment 30 is presented with the same line characteristics found in
the PSTN. Thus, in the all DSL operating state, the DVB 24 is able to
provide the same impedance and central office line voltage levels for
which the POTS equipment 30 was designed to operate.
When the switching mechanism 22 creates a signal path through the analog
terminal 23, the switching mechanism 5 in the central office switching
equipment 1 creates a path with the analog terminal 3 thereby establishing
a typical voiceband connection. This operating condition is often referred
to as the "life line" state since the call switching equipment 1 presents
a constant source of line voltage (typically 48 volts) which allows the
POTS 30 at the subscriber site to be utilized even in times when the power
is interrupted. According to the invention, the switching mechanisms 5 and
22 are configured to permit life line operation of the POTS 30 so that
communications are maintained in the event power is lost on the subscriber
side of the network. Thus, the central office call switching equipment 1
and remote terminal 20 include the capability of providing the identical
line characteristics to the POTS 30 even in the all DSL operating states,
eliminating the standard requirement for upgrading POTS equipment to
operate properly with the context of the invention.
In addition, the invention contemplates maintaining the line impedance
voltage characteristics as the POTS 30 transitions from on-hook to
off-hook, during retrain or power cutbacks, data rate reductions of the
DSL compliant device 28 and other operating conditions of the remote
terminal 20. In the all DSL operating state, the switching mechanisms 5
and 22 act to disconnect the power supply at the CO 1 and permit the POTS
30 to be connected directly to the remote terminal 20 or a DSL modem
incorporating the functionality and architecture of the remote terminal
20.
Turning now to FIG. 2, the general architecture of the DVB 7 in the CO 1 is
shown. The DVB 7 includes three terminals 41, 45, and 47 and a control
interface 51. In particular, terminal 41 provides a signal pathway for
voiceband signals communicated between voice frequency interface 4 and DVB
7. Terminals 45 and 47 form the signal paths of the communications link
13. In the downstream direction, voiceband signals from the voice
frequency interface 4 reach the hybrid circuit 42 which provides the
2-wire to 4-wire interface mechanism within the CO switching equipment 1.
In the all DSL operating state, voiceband signals are directed to the band
pass filter 43 which performs the voiceband filtering and anti-aliasing
functions on the incoming analog signals and presents a band-limited
voiceband signal to the analog-to-digital (A/D) converter 44. The A/D
converter 44 can sample the incoming analog signal and create a digital
representation of the signals at terminal 45. The digital signals are then
made available to the DSL compliant device 10 through communications link
13.
In the upstream direction, digitized voiceband signals arrive into the DVB
7 via the terminal 47 and pass through digital-to-analog (D/A) converter
48 and then through low pass filter 46 and into the hybrid circuit 42. The
converted signal wave forms then reach the voice frequency interface 4
through terminal 41.
Also found within the DVB 7 is a ring detect and hold circuit 49 which
permits the DVB 7 to determine when an incoming call is received at the CO
1. The implementation and utilization of the ring detect and hold circuit
49 is well known to those of ordinary skill. A control and signaling
function 50 is provided within the DVB 7 which allows external operation
of the DVB 7 depending on the operating state of the central office
switching equipment 1. The DVB 7 is connected to the switching system 2
within the central office equipment 1 through the voice frequency
interface 4 when the DSL compliant device 28 is turned ON. The DVB 7 can
emulate a telephone set by providing ring detection and signal hold at the
ring detect hold circuit 49. Thus, all voiceband signals can be digitized
and transmitted using the DSL compliant device 10.
The general architecture of the DVB 24 within the remote terminal 20 is
shown in more detail in FIG. 3. An important aspect of the remote terminal
20 is that it be able to deliver similar transmission line characteristics
which the POTS equipment 30 is used to seeing This aspect of the invention
is provided through the battery feed, off-hook detect ring trip detect and
ring generator circuit 60 which emulates many of the functions of a
typical central office facility. For example, the line voltage over a
typical PSTN wire line pair is 48 volts from the CO 1 to the POTS 30 at
the subscriber side of the loop. Battery feed circuit 60 can provide such
typical line voltages (with appropriate line losses) so that the POTS 30
is powered up in the off-hook state when the remote terminal 20 is
operating in the all DSL state.
The voice frequency interface 25 is coupled to the DVB 24 at terminal 62
and reaches the hybrid circuit 64. The hybrid circuit 64 performs a 4 wire
to 2 wire conversion on signals delivered to the DVB 24 through terminal
62. In the all DSL operating state, the voiceband signals are directed to
the band pass and A/D block 66 which performs in a similar fashion to like
components in the DVB 7 within the CO 1. The output of block 66 is
directed to terminal 70 which is coupled to the DSL compliant device 28
through signal path 32 in the remote terminal 20. Terminals 70 and 72
represent the signal paths of the communications link 32 coupling the DVB
24 to the DSL compliant device 28.
In the downstream direction, digital signals from the DSL compliant device
28 arrive into the DVB 24 through terminal 72. These digital signals are
digitized representations of voiceband signals intended for the POTS
equipment 30. The digital signal stream enters the converter and filter
section 68 within the DVB 24. In particular, block 68 within the DVB 24
performs similar functions to the components 46 and 48 within the DVB 7 of
the central office 1. The output of block 68 are analog signals within the
voiceband which are directed to the hybrid circuit 64 where they are
eventually transferred to the voice frequency interface 25 of the remote
terminal 20.
Turning to FIG. 4, therein is shown a wiring configuration for an in-house
four wire connection suitable for use with the remote terminal 20. A
single wire line pair 21 is coupled to the voice frequency interface 25
within the remote terminal 20. The switching mechanism 22 comprises two
independent switches 80 and 82 which toggle depending on the operating
state of the remote terminal 20. Thus, in the all DSL operating state, the
switches 80 and 82 form signal paths from the high frequency interface 27
to the wire line pair 21.
In the all-DSL operating state, the DSL data stream enters the DSL
compliant device 28 where it is processed and decomposed into its
voiceband (VB) and digital data (DD) components. The VB component is
relayed to the DVB 24 which, in turn, is coupled to a second wire line
pair 23 found in common subscriber site installations. Thus, the wiring
configuration of FIG. 4 takes advantage of the second wire line pair 23
which often goes unused or is reserved for emergency based services such
as automatic alarm and burglar detection systems.
As before, the DVB 24 presents typical power supply and line
characteristics which the POTS equipment 30 requires for proper operation
according to its design. The VB component of the DSL data stream is
received by the POTS equipment 30 through the voice frequency interface 25
which is unaware of its origin.
The DD component of the DSL data stream is transferred to the digital
interface 29 and is made available to a digital data device 31 which can
be a computer, workstation, digital receiver or other similar digital
component. Given the rapidly emerging DSL applications, it is envisioned
that the digital data device 31 can comprise a wide array of equipment
utilized at the subscriber premises designed to utilize any one or more of
the DSL variant protocols.
In one embodiment, the voice frequency interface 25 includes a special jack
84 which allows the POTS 30 to utilize the unused wire line pair 23. The
jack 84 would couple the pins on the plug from the POTS equipment 30
(usually an RJ-11 plug) to the unused pair 23. In other embodiments, the
voice frequency interface 25 can employ other switching techniques in
order to connect voiceband signals from the POTS to the DVB 24 in the all
DSL operating state of the remote terminal 20 to equipment 30 make the
connection.
FIG. 5 shows an alternative wiring configuration for the remote terminal 20
according to still another embodiment of the invention. The switching
mechanism 22 still comprises two separate switches 80 and 82 which
determine the operating state of the remote terminal 20 as well as the
signal path of signals to and from the remote terminal 20. The distinction
lies in the use of multiple voice frequency interfaces 25a and 25b which
are used to couple the digital data device 31 and POTS 30, respectively,
to the in-house wire line pairs 21 and 23. Thus, the transitions from a
voiceband operating state to the all DSL operating state occurs as
switches 80 and 82 toggle from the high frequency interface 27 and the
typically unused wire line pair 23.
The configuration of FIG. 5 presumes that the remote terminal 20 operates
in the all DSL operating state or that the CO call switching equipment 1
is able to decipher the incoming data stream arriving from the digital
data device 31 or the POTS equipment 30 over the wire line pair 21 when
the remote terminal 20 is operating in normal voice band.
The wiring configuration of FIG. 5 is contrasted with the configuration
shown in FIG. 6 wherein the primary connection to the central office is
now the typically unused wire line pair 23. In this case the voice
frequency interface 25 can present the exact jack configuration which the
POTS equipment 30 is designed to accept. The switching mechanism 22
handles the transition between states by switching the incoming wire line
23 from the CO 1 between the standard utilized wire line pair 21 when the
DSL compliant device 28 is turned OFF to the high frequency interface 27
when the compliant device 28 is ON. Thus, in the all DSL operating state,
the DVB 24 receives signals from the standard wire line pair 21 and drives
the POTS equipment 30.
Another embodiment of a wiring configuration within the subscriber premises
is illustrated in FIG. 7. In this embodiment, the DSL compliant device 28
and POTS equipment 30 are utilizing the same wire line pair 21 found in a
typical business installation. The voice frequency interface 25 can behave
as a low pass filter passing only those signal components within the voice
band. Since all signal traffic is directed into the DVB 24, it is assumed
that the DSL compliant device 28 is always ON providing a continuous DSL
operating state of the remote terminal 20. This is a good configuration
for voice over IP applications where all voice data is carried from end to
end in a digital format.
While the invention has been described with reference to preferred
embodiments it should be understood that modifications will become
apparent to those of ordinary skill of the art and that such modifications
are intended to be included within the scope of the invention as defined
by the following claims.
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